We have recently isolated a cell strain (L-2) from adult rat lung by clonal culture techniques. In vitro, these cells retain osmiophilic lamellar bodies in their cytoplasm that are morphologically identical to those present in type II alveolar epithelial cells in whole lung (1-3). We propose to monitor rates of pulmonary surfactant (saturated lecithin) biosynthesis by monolayer cultures of L-2 cells. The cells will be treated with various agents known to inhibit or stimulate surfactant production. By using inhibitors of surfactant biosynthesis we will terminate surfactant production and then determine agents that are most effective in reinitiating synthesis in the surfactant deficient cells. This approach is designed to mimic the in utero environment in children afflicted with idiopathic respiratory distress syndrome where type II cells do not produce surfactant. The influence of hormones and other agents on pulmonary surfactant production will be quantitated by measuring the rate of incorporation of 14C-choline into saturated lecithin. In addition we will investigate the effects of various agents on the following parameters of the L-2 cells in culture: growth rate, size and number of lamellar bodies per cell, lipid composition, secretion of the surfactant into the culture media, changes in specific activity of three enzymes in the choline incorporation pathway and changes in surfactant-associated esterase patterns. Information derived from these studies will be of clinical signficance for the care and treatment of premature infants afflicted with respiratory distress syndrome.